The present invention relates to space and communications satellites, and more particularly, to a method for operating a satellite to prevent physical interference between a satellite that experiences a control loss with operating satellites in orbit.
Satellites in geostationary orbits (GEO) have been widely preferred for several decades because of the economic advantages afforded by such orbits. In a geostationary orbit, a satellite traveling above the Earth""s equator, in the same direction as the Earth is rotating, and at the same angular velocity, appears stationary relative to a point on the Earth. These satellites are always xe2x80x9cin viewxe2x80x9d at all locations within their service areas, so their utilization efficiency is effectively 100 percent. Antennas at Earth ground stations need be aimed at a GEO satellite only once; no tracking system is required.
Coordination between GEO""s and terrestrial services is facilitated by governmental allocation of designated xe2x80x9cslotsxe2x80x9d angularly spaced according to service type. Given the desirability of geostationary satellite orbits and the fact that there are only a finite number of available xe2x80x9cslotsxe2x80x9d in the geostationary xe2x80x9cbelt,xe2x80x9d the latter capacity has been essentially saturated with satellites operating in desirable frequency bands up through the Ku-band (up to 18 GHz).
When geostationary satellites approach the end of their useful life, the fuel supply is usually also near depletion. Operators, by mutual agreement, deorbit the spacecraft by raising its altitude above the synchronous radius. This causes the spacecraft to drift harmlessly around the earth for eternity.
It is assumed in this process that attitude and orbit control is possible. If a satellite loses attitude control, the satellite may drift or oscillate in longitude back to the synchronous radius and, thus, may pose a threat of collision with active satellites in the geostationary belt. Radar tracking is required to insure that satellites do not collide, or to provide information to operators so that evasive maneuvers may be performed to avoid collisions.
Other satellites may have redundant control systems which are not fully functional. That is, only one set of electronics may still be operable in an older satellite. Such satellites may also have weakened or non-functional batteries. These satellites are marginally operable satellites. The risk with marginally operable satellites is that during an eclipse, the satellite may lose the control electronics. If this occurs, the satellite may enter another orbital path and pose a risk for other geostationary satellites.
It may also be desirable to place a satellite into an orbit other than the geostationary belt. This may be useful if the particular satellite is no longer needed. However, as previously mentioned above, satellites are typically increased in altitude. By increasing the altitude of the satellite, the satellite shifts by about 1.520  a day to the west with respect to the earth. To move a satellite back into its original position if its use is again desired, a significant amount of fuel may be required. However, it is possible that sufficient fuel may not be available for repositioning the satellite.
It would therefore be desirable to provide a method of operating a satellite that allows marginally operating satellites to remain in service without threatening satellites in the geostationary belt.
It is therefore an object of the present invention to provide a satellite system that allows for the operation of a satellite in a substantially geostationary orbit so that it will not collide with other geostationary satellites in use should on-board systems ultimately fail.
In one aspect of the invention, a satellite system that is coordinatable with a geostationary belt having a plurality of geostationary positions includes an eccentric satellite orbit having a predetermined angle of inclination with respect to the equatorial plane and a non-coincident equatorial crossing node with the geostationary belt.
In a further aspect of the invention, a method of positioning a satellite comprises the steps of: providing a satellite into a geostationary belt; and, positioning the satellite in a substantially geosynchronous (24 hr. period) second orbit so that the second orbit is eccentric non-intersecting with said geostationary belt upon the sensing of a predetermined condition indicative of an impending failure on-board the satellite.
One advantage of the invention is that after the satellite is moved into the second orbit, the satellite may still be easily tracked and communicated with with the use of a stationary antenna.
The satellite may then be moved back into a standard GEO if the satellite is desired to be used. Moving the satellite back may be particularly useful for a marginally operating satellite that is entering eclipse season. When a satellite is in an eclipse, the power is lost. If the battery or communication circuitry fails, the satellite may drift in orbit without being capable of adjustment. Eventually the satellite may collide with other operational satellites.
Other objects and features of the present invention will become apparent when viewed in light of the detailed description of the preferred embodiment when taken in conjunction with the attached drawings and appended claims.